Needle size for socks

So, yarn I bought from ebay doesn't actually have a size on it. Here is what the product says at the store website, though.

Recommended gauge is 7 st/1" on a size 3 needle.

I want to try the universal sock pattern from knitty, and was wondering if I should change sizes to make a sock. I was thinking I should probably go down to a 1, since I don't want airy socks and it was airy when I knit it up on a 3. Another question: when I'm at the store, if I bought some nylon thread to enforce the heel and toes, do I just knit as two strands together? and would elastic knit on the last part of the top be beneficial?